If I'm not mistaken, these actions were made of wrought iron. A thin layer of carbon may have been added by case hardening, but I don't believe wrought iron had any carbon in it to make it a steel. I believe wrought has a stringy pattern just on its own.
I think the finer the lines that show, chances are the more the wrought was forged out to reduce the effect those lines may have on the integrity of the final part. I suspect the difference in appearance is from components other than carbon. Chances are, forging different carbon content steels together ends up evening the carbon content between the two.
Craig,
Wrought iron is not a material that is typically compatible with forging as it can have a tendency to crack when hot forged. It was as close to pure iron as was available at the time (.10-.25%). I think what we're looking at with these actions is early Bessemer steel with contaminants or constituents that weren't homogenized.
